Implemented subcast_key on dict (#152)

* implemented subcast_key on dict

* Add TODO to rename arg

* Fix typing

* Update changelog

Co-authored-by: Steven Loria <sloria1@gmail.com>

Author: AugPro

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 7.4.0 (unreleased)
+
+- Add `subcast_key` argument to `env.dict` ([#151](https://github.com/sloria/environs/issues/151)).
+  Thanks [AugPro](https://github.com/AugPro) for the suggestion and PR.
+
 ## 7.3.1 (2020-03-22)
 
 - Fix error when parsing empty list with subcast
@@ -240,7 +245,3 @@ Bug fixes:
 ## 0.1.0 (2016-04-25)
 
 - First PyPI release.
-
-```
-
-```

environs/__init__.py

@@ -143,13 +143,19 @@ def _preprocess_list(value: typing.Union[str, typing.Iterable], **kwargs) -> typ
 
 
 def _preprocess_dict(
-    value: typing.Union[str, typing.Mapping[str, _T]], subcast: Subcast, **kwargs
-) -> typing.Mapping[str, _T]:
+    value: typing.Union[str, typing.Mapping],
+    # TODO: Rename subcast to subcast_values and re-order arguments for next major release
+    subcast: Subcast,
+    subcast_key: Subcast = None,
+    **kwargs
+) -> typing.Mapping:
     if isinstance(value, Mapping):
         return value
 
     return {
-        key.strip(): subcast(val.strip()) if subcast else val.strip()
+        (subcast_key(key.strip()) if subcast_key else key.strip()): (
+            subcast(val.strip()) if subcast else val.strip()
+        )
         for key, val in (item.split("=") for item in value.split(",") if value)
     }
 

tests/test_environs.py

@@ -107,6 +107,14 @@ def test_dict_with_subcast(self, set_env, env):
         set_env({"DICT": "key1=1,key2=2"})
         assert env.dict("DICT", subcast=int) == {"key1": 1, "key2": 2}
 
+    def test_dict_without_subcast_key(self, set_env, env):
+        set_env({"DICT": "1=value1,2=value2"})
+        assert env.dict("DICT") == {"1": "value1", "2": "value2"}
+
+    def test_dict_with_subcast_key(self, set_env, env):
+        set_env({"DICT": "1=value1,2=value2"})
+        assert env.dict("DICT", subcast_key=int) == {1: "value1", 2: "value2"}
+
     def test_dict_with_default_from_string(self, set_env, env):
         assert env.dict("DICT", "key1=1,key2=2") == {"key1": "1", "key2": "2"}